1. Field of the Invention
The present invention relates to a digital broadcast receiver and to a method of controlling reception of digital broadcasts and, more particularly, to a digital broadcast receiver equipped with a plurality of decoders and also to a method of controlling reception of digital broadcasts using this receiver.
2. Description of the Related Art
In the past, in a digital broadcast receiver having only one decoder, the following operations have been performed when one service (digital broadcast program) is viewed and listened to. A received, encoded signal of a digital broadcast program is decoded by one video/audio decoder, and the decoded signal is distributed to the output for viewing and output for recording. A so-called, dual-decoded digital broadcast receiver equipped with two decoders is available as an extension of the aforementioned digital broadcast receiver. Also, in this case, when one service is viewed and listened to, a received encoded signal of a digital broadcast program is decoded by one decoder and distributed to the output for viewing and output for recording.
A related art digital broadcast receiver is described below in detail with reference to drawings.
FIG. 3 shows a block diagram of a related art digital broadcast receiver. In FIG. 3, a receiver unit 101 is equipped with front ends 102 and 103. The front end 102 corresponds to multichannel terrestrial airwaves received at an antenna (TER. antenna) for terrestrial digital broadcasts, while the other front end 103 corresponds to an antenna for BS (Broadcasting/Satellite)/CS (Communications Satellite) (hereinafter abbreviated BS/CS) digital broadcasts. Each front end tunes in to one channel either out of multiple channels of terrestrial airwaves received or out of multiple channels of BS/CS TV received and demodulates the channel into a signal that can be image-processed. Another receiver unit 121 is also equipped with front ends 122 and 123 and has functions similar to those of the receiver unit 101.
A selector unit 114 is equipped with switches 104 and 124 and makes a choice between terrestrial airwaves and BS/CS broadcasts based on a user's instruction. In this example, the switch 104 selects the terrestrial TV front end 102, whereas the switch 124 is not in use.
Descramblers 105 and 125 are devices for performing descrambling making use of key information in an IC card portion. Multiplex/demultiplex units (MUX/DEMUX) 106 and 126 extract audio and video signals, superimposed character information, electronic (or electric) program guide (EPG) information, control signals, and other information from the descrambled digital broadcast downstream data.
Audio/video decoders (AV decoders) 107 and 127 are devices for decoding the encoded audio and video signals extracted by the multiplex/demultiplex units 106 and 126. Graphics units 108 and 128 process the superimposed character information sent from a CPU (described later). In some forms of the graphics units 108 and 128, they directly receive the superimposed character information from the multiplex/demultiplex units 106 and 126 and process the information in a given manner. Adders 109 and 129 superimpose the character information delivered from the graphics units 108 and 128 onto the video signals delivered from the audio/video decoders 107 and 127, respectively.
A display layout unit 110 is a device for outputting the audio signals from the audio/video decoders 107 and 127 and the video signals from the adders 109 and 129 on which the character information has been superimposed, according to the form of display on a display device (not shown) connected for viewing.
In a case where the display device (not shown) has a function of displaying plural pictures on a single display screen, for example, the display layout unit 110 displays only one of plural pictures when the display device is in the single-picture mode. When the display device is in the dual-picture mode, the display layout unit displays the two images on the display screen, thus achieving dual picture display. When two or more pictures are displayed, the graphics unit 111 controls the arrangement of the superimposed characters.
The audio signal from the audio/video decoder 107 and the video signal from the adder 109 on which the character information has been superimposed are output to a recording device (not shown) via a switching unit 115 for recording purposes. The switching unit 115 has switches 116 and 117 and connects the switches 116 and 117 either with the audio/video decoder 107 or with the audio/video decoder 127 according to a user's instruction such that the output for recording is supplied to the recording device. The signal entered for recording into the recording device is recorded as recorded data in a nonvolatile recording device (not shown).
Key information for performing descrambling in a limited reception method such as a conditional access (CA) system is recorded in an IC card portion 131. A modem 132 is a device, for example, which when personal information about users and information about fees are sent to a broadcast provider in a pay broadcast service, makes an access to the Internet from the modem via a telephone network and performs bidirectional communication of information. A CPU (central processing unit) 133 is a device for controlling the whole digital broadcast receiver. For example, the CPU provides control to switch the decoders according to a program loaded in a ROM (read-only memory) 134. A RAM (random access memory) 135 is a memory acting as a working area for the CPU 133. A nonvolatile memory (NVM) 136 is a memory for storing, for example, a channel number viewed by the viewer immediately before the power supply was turned off last time.
These IC card portion 131, modem 132, CPU 133, ROM 134, RAM 135, and nonvolatile memory 136 are connected by a bus (control line) 130 to permit data communications among them. Connected with the bus 130 are the front ends 102, 103, 122, 123 of the receiver units 101, 121, descramblers 105, 125, multiplex/demultiplex units 106, 126, audio/video decoders 107, 127, graphics units 108, 128, display layout unit 110, and graphics unit 111. The CPU 133 controls the above-described various portions via the bus 130.
In the above-described digital broadcast receiver of FIG. 3, the signal path line passing through the receiver unit 101, descrambler 105, multiplex/demultiplex unit 106, and audio/video decoder 107 is hereinafter referred to as the path line A. The signal path line passing through the receiver unit 121, descrambler 125, multiplex/demultiplex unit 126, and audio/video decoder 127 is referred to as the path line B. In FIG. 3, a service received through the receiver unit 101, descrambler 105, multiplex/demultiplex unit 106, and audio/video decoder 107, i.e., path line A, is distributed to the output for viewing and output for recording.
In the state shown in FIG. 3, when the user wants to record the received service, video and audio signals for recording are output from the audio/video decoder 127 to the recording output terminal. The signals are recorded in the recording device (such as a video tape recorder) connected with the terminal. At this time, the recording output side is not allowed to switch the video and audio signals to other service or other downstream data until the recording is complete. In this way, variation in the state is restricted because of the specifications of the product. Under this state, if the user wants to view and listen to a service which is being offered by the same digital broadcast but is not being recorded and if the user switches the service or stream data, processing for disconnecting the decoder in the path line A is preferably performed.
In particular, in FIG. 3, there may arise the need to decode a service (to be viewed) not recorded by the audio/video decoder 127 by switching the switch 124 and connecting the terrestrial TV front end 122 and descrambler 125. The display layout unit 110 may need to switch the displayed content from the video and audio signals from the audio/video decoder 107 to outputting of the video and audio signals from the audio/video decoder 127. In this case, the timing at which the viewed service is switched is identical with the timing at which the device is switched from one to another. Therefore, no special problems occur in terms of the specification of the product.
Also, a digital broadcast receiver has been proposed which is capable of recording programs different from the program being displayed and which permits one to select these programs easily using a program guide; then the programs can be displayed or recorded (for example, see patent reference 1).
Patent Reference 1: JP-A-11-18020